Light sensors are used in many applications to detect the presence of objects. A light sensor typically has a light emitter that emits light and a light receiver that receives and detects the light emitted by the emitter. The emitter and receiver are placed across a region where the detection of objects is sought, which creates a light path between the emitter and the receiver. When an object enters the region, the object interrupts the light path between the emitter and the receiver, which is detected by associated electronics. The light sensor then transmits an indication that an object is located in the region.
One use of light sensors is in an autochanger. An autochanger is a mass data storage device having a plurality of media pieces and media players located therein. The media pieces are retained within the autochanger in a plurality of media holding bays. A media handling device, sometimes referred to as a picker, transports the media pieces between the holding bays and the media players. In order to decrease the size of the autochanger, the picker operates in close proximity to the holding bays and, thus, the media pieces. In the event a media piece becomes dislodged from its media holding bay, the picker will likely collide with the media piece. This collision may damage the picker, the media piece, and other components within the autochanger. Examples of autochangers are illustrated in U.S. Pat. No. 5,043,962 of Wagner et a. for CARTRIDGE HANDLING SYSTEM and U.S. Pat. No. 5,719,833 of Jones for APPARATUS FOR SECURING A CARTRIDGE ENGAGING ASSEMBLY WITHIN A CARTRIDGE HANDLING SYSTEM, both of which are hereby incorporated by reference for all that is disclosed therein.
In order to assure that the media pieces have not become dislodged from the media holding bays, a light sensor is used to detect the presence of media pieces and other obstructions in the path of the picker. A light emitter emits a beam of light in front of the media pieces and a receiver detects the light. Accordingly, a light path is formed between the emitter and the receiver and adjacent the media holding bays. In the event that a media piece becomes dislodged, it will cross the light path, disrupting the light beam. This disruption is sensed by the receiver and transmitted to a processor within the autochanger. An indicator may be displayed to notify an operator of the problem. Additionally, the autochanger may function in a manner that prevents the picker from traveling in the region of the dislodged media piece.
Many of the media holding bays within the autochanger are arranged in columns and have separate light sensors associated with each column. One problem encountered with using a separate light sensor with each column is that the light beams fan out from their sources. Therefore, as the number of media holding bays in the columns increases, the amount that the light beams fan increases. The increased fanning of the light beams increases the sizes of each light beam associated with each column. These large light beams cause problems with cross talk between individual light sensors. For example, light emitted by a first emitter associated with a first column may be detected by a second receiver associated with a second column. If a media piece located in the second column becomes dislodged, the second receiver may still receive light from the first emitter. Accordingly, the autochanger will not detect the dislodged media piece and may drive the picker into the dislodged media piece.
Another problem with a fanning light beam is that the intensity of the light beam significantly attenuates from the source. Accordingly, as the distance between an emitter and a detector increases, the intensity of light received by the receiver decreases. In addition, the intensity of the light may vary throughout the light beam. This presents problems in the detection of the light emitted by the emitter. For example, circuitry that monitors the output of the receiver may have a threshold wherein an output above the threshold indicates that the light beam has not been disrupted and an output below the threshold indicates that the light beam has been disrupted. The reduced intensity of light in the fanned light beam requires that the threshold be set relatively low. Another problem occurs if an emitter becomes misaligned, even by a relatively small amount relative to its corresponding receiver. The misalignment may cause the receiver to receive light from a portion of the light beam that has a relatively low intensity. Accordingly, the output of the receiver may not be greater than the threshold, which will cause a false indication that the light beam has been disrupted and that a media piece has become dislodged.
A need exists for a peripheral device that overcomes some or all of these problems.